This invention relates to an adjusting device for fuel injection valves, and more particularly to an adjusting device for adjusting the initial injection lifts of double-injection type fuel injection valves.
In a conventional diesel engine, there is a problem that while the fuel injection rate, i.e. injection quantity per unit time should be set at a suitably high value for improvement of the output characteristics of the engine as well as prevention of the emission of nitrogen oxides, an increased fuel injection rate can lead to a correspondingly shortened injection period, which causes a reduction in the combustion duration, resulting in a combustion noise, and can also cause an increase in maximum pressure within the engine cylinders, as well as irregular fuel injection.
To solve the above problem, fuel injection valves have been proposed by the assignee of the present application in U.S. Pat. No. 4,390,129 issued June 28, 1983 and Japanese Provisional Utility Model Publication No. 57-145760 issued Sept. 13, 1982, which are a double-injection type having first and second nozzle springs, wherein fuel injection takes place in two steps in such a manner that the first nozzle spring is compressed by an initial injection valve opening pressure to cause lifting of the nozzle needle for initial injection, and subsequently the first and second nozzle springs are both compressed by a main fuel injection valve opening pressure to cause further lifting of the nozzle needle for main injection. This double injection reduces the injection rate through the whole injection period, thus substantially overcoming all the aforementioned drawbacks of combustion noise, emission of nitrogen oxides and irregular injection.
The above proposed double-injection type fuel injection valves commonly comprise a first movable spring seat coupled to a nozzle needle for lifting therewith and supporting the first nozzle spring, a second movable spring seat supporting the second nozzle spring, a seat held stationary at a predetermined axial location and on which the second movable spring seat is seated, a shim interposed between the seat and the second movable spring seat for maintaining the second movable spring seat in its seated position spaced from the first movable spring seat in its seated position by a preset gap determining a desired initial injection lift, and a hollow member accommodating at least the second nozzle spring.
In these double-injection type fuel injection valves constructed as above, the operation of adjusting the above gap determining the initial injection lift is rather complicated and troublesome if it is made by the use of conventional adjusting means. Further, it is difficult to adjust the gap to a correct value with accuracy by the use of conventional adjusting means.